In view of the wide variety of products that are dispensed from containers, numerous constructions have evolved for container closures, including, for example, screw caps, stoppers, corks and crown caps, or the like. Generally, products such as vinegar, vegetable oils, laboratory liquids, detergents, honey, condiments, spices, alcoholic beverages, and the like, impose similar requirements on the type and construction of the closure means used for containers for these products. However, wine sold in bottles represents the most demanding product in terms of bottle closure technology, due to the numerous and burdensome requirements placed upon the closures used for wine bottles. In an attempt to best meet these demands, most wine bottle closures or stoppers have historically been produced from a natural material known as “cork”.
While natural cork still remains a dominant material for wine closures, synthetic wine closures have become increasingly popular over the last years, largely due to the shortage in high quality natural cork material and the problem of wine spoilage as a result of “cork taint”, a phenomenon that is associated with natural cork materials. In addition, next to synthetic cork stoppers, there has recently been a growing acceptance and use of screw caps as closures for wine bottles. These caps are particularly advantageous due to their relatively low cost, the avoidance of “cork taint” with this type of bottle closure, and the possibility to achieve an airtight, hermetic seal.
Most screw caps contain a liner so as to achieve a substantially airtight, substantially hermetic seal between the closure and the bottle. Such a seal prevents substantially any oxygen transfer through the bottle closure. For certain types of wines, especially white wines, conventional air-tight screw-caps may be the closure of choice, as ingress of oxygen impairs the fresh and fruity appeal of these wines, which are usually meant to be consumed young. However, for other types of wines, such as premium class red wines, it is desirable to strike a delicate balance between tightly sealing the bottle content to prevent leakage, avoid contaminants, counteract degradation and spoilage by oxidation, on the one hand, and, on the other hand, permitting a restricted amount of oxygen to enter the container, so as to ensure full maturation of the wine flavor characteristics and prevent the formation of unpleasant aromas. Recent scientific studies appear to confirm what was already accepted empirical knowledge in the traditional art of winemaking: that oxygen is intimately involved in the aging and maturation process of wine. If certain types of wines are completely starved of oxygen for long periods of time, a process known as reduction may give rise to malodorous sulfur compounds such as certain sulphides, thiols and mercaptans. To prevent reduction over the entire period of wine aging and maturation, a minute but constant concentration of oxygen within the container interior is necessary. The olfactory defect occurring otherwise is sometimes referred to as reduced character and can be readily identified by the presence of odors reminiscent of rotten egg, garlic, stagnant water, burnt rubber, struck matches and/or cooked cabbage. Even at low concentrations, these odors may completely ruin a wine's character.
Therefore, bottle closures that ensure a hermetic seal, such as crown or screw caps, are usually not recommended for bottling of wines which require a certain amount of oxygen (from an organoleptic point of view) to diffuse into the interior of the closed bottle. This is the reason why natural cork stoppers—and not screw caps—have been used as closures of choice by many generations of winemakers. Conventional screw caps on the other hand, are used preferentially for bottling wines that are intended for more immediate consumption, in which this aging period is not required or desired. As mentioned hereinbefore, the use of hermetic, airtight closures for wines intended for long periods of aging in the bottle may give rise to reduction processes, which may compromise the organoleptic properties of the wine.
To be able to leverage the advantages of using screw caps also when closing higher quality wines, which need limited oxidation for full organoleptic maturation, closure technology has been developed that allows for controlled ingress of oxygen through microperforated screw cap liners. The total amount of oxygen that the bottled wine will be exposed to depends on the elapsed time period before consumption. There may be a great degree of variation depending on whether the wine was consumed early after bottling or was stored for several years before consumption. Moreover, the method of manufacturing said microperforated breathable screw cap liners is quite labor- and cost-intensive.
There is a need for closures with a defined amount of oxygen being supplied to the bottle content without running the risk of spoilage by either uncontrolled oxidation or complete lack of oxygen, i.e., reduction.